High quality silage: a must for beef production systems

• Defining targets for grass silage production
• First cut silage quality targets for different stock types
• Finding the right balance between yield and quality
• Management guidelines for cost-effective grass silage production

Summary

• National average silage dry matter digestibility (DMD) remains at 66%. This is suitable only for dry suckler cows in good body condition.
• To achieve good performance on silage diets, growing/finishing cattle and calved suckler cows require silage of at least 74% DMD. Consider quality and quantity together in feed plans.
• Cutting swards at the correct growth stage determines silage quality. Soil fertility, reseeded swards and correct rates of nitrogen application are the key elements to maximizing silage quality and quantity across the season.
• Completing a fodder budget after first-cut is advised to plan ahead for feed security next winter.

Introduction

Grass silage typically makes up around one quarter to one third of total feed dry matter (DM) consumed on drystock farms. Compared to grazed grass it is quite expensive to produce (usually twice the cost per tonne DM), however when taken as part of an integrated grazing system it is good value compared to concentrates and alternative forages.

Recent experiences with national fodder shortages have underlined the value of having a good reserve of quality silage available on beef farms. Teagasc national fodder surveys in 2020-21 showed that while the majority of beef farms had adequate silage reserves (i.e. 15-20% relative to winter demand), a cohort of 10-12% of farms are consistently running a significant feed deficit of more than 20% of winter requirements. This is a high-risk strategy, especially during periods of fodder scarcity and high input prices. It is likely to be particularly expensive for these farms to bridge deficits with purchased forage and/or concentrates in the winter of 2022/23.

Early intervention to correct shortages is advised, starting with completing a winter feed budget. While most beef farms have tended to secure adequate supply of silage tonnage in recent years, average silage quality (as measured by dry matter digestibility, DMD) remains consistently poor on drystock farms at 65-67% DMD. The principal challenge for beef producers therefore is to balance the dual objectives of having adequate supply of silage, while meeting feed quality targets for good animal performance.

Defining targets for grass silage production

The three key elements to cost effective grass silage production are:

1. High grass DM yields for first-cut and subsequent cuts, with high total annual grass yield (>14.0 tonnes DM/ha). Guideline yields are 4.8 t DM/ha and up to 6.2 t DM/ha for silage harvested in mid-May and early June, respectively.
2. Appropriate feed quality for the category of stock to be fed. This is best measured as digestibility of the crop dry matter (DMD); protein content is also important and is positively associated with DMD. Silage quality is a function of growth stage at cutting (leafy swards have higher DMD than stemmy swards).
3. Clean, stable feed with good intake potential. This is achieved through good fermentation and can be assessed from silage pH (3.9 to 4.2 for un-wilted crops), ammonia (target less than 9%), and lactic acid (target over 8%) content. High DMD (leafy) swards can be well-preserved with good management.

First cut silage quality targets for different stock types

Grass DM yield at harvest is the single most important factor determining the cost per tonne of silage in the pit. Fixed costs per hectare (e.g. land charges, contactor fees) may be diluted over the extra tonnage for a given cut, and so too are some variable costs associated with fertiliser and slurry applications.

Many beef farms have largely abandoned any consideration of feed quality when planning first-cut silage crops, focussing only on feed ‘bulk’. Dry suckler cows can be adequately fed on 67-68% DMD grass silage. However, for growing/finishing cattle and suckler cows suckling calves the target is to have silage at 72- 74% DMD or higher.

The effect of silage quality (DMD) on animal live weight performance was assessed by a study carried out at Grange, where a silage sward was harvested at four different dates and fed to growing cattle the following winter (Table 1). While first-cut yield was lower with earlier cutting as expected, average daily live weight gain was much improved on the leafy silage. Feeding the higher quality (75% versus 65% DMD) silage at farm level would result in approximately 40 kg extra live weight gain over a 150-day housing period, or 2.0 to 2.5 kg reduction in daily concentrate intake for similar daily gain. In fact, it took less than half the amount of silage DM to achieve 1 kg carcass gain with the better quality sward.

Table 1. Effect of silage quality (dry matter digestibility, DMD) on daily weight gain and feed efficiency in growing cattle

It is clear therefore that poor silage quality is a major limitation to growing animal performance over the winter period on many farms. Feeding low DMD silage made for ‘bulk’ may actually contribute to a silage shortage in the long-term, because animals require more days on-farm in the subsequent grazing season to achieve a given final carcass weight, reducing area available for silage cutting. Furthermore, delaying first-cut will limit yield and/or delay date of second-cut silage, resulting in a potential reduction in annual forage yield per hectare. Management decisions around first-cut date should prioritize meeting DMD targets and improving annual grass tonnage per hectare, rather than focussing solely on the yield from first cut.

Finding the right balance between yield and quality

While growing cattle require silage made from leafy swards, there is a risk of unnecessary/ excess body condition gain for late-gestation suckler cows offered this type of feed. Beef farms with a mix of stock types (e.g. dry suckler cows, weanlings and finishing cattle) must plan for making silage at varying DMD levels. Differences in silage DMD can be created by varying the cutting date within a well-managed grass sward.

High quality silage is produced by cutting in mid-May when grass has high leaf content, while lower DMD silage is produced by delaying cutting into early June when grass has become ‘stemmy’ after seed head emer­gence. Therefore, while the objectives of good DM yield and excellent preservation remain consistent, target DMD should dictate the optimum stage of grass maturity at which to har­vest the crop.

The practical reality for beef farms feeding varied stock types over the winter is that no single cutting date is suitable for all stock. A simple silage management plan that takes this into account can be developed for the farm, using the following steps:

1. Define the highest quality silage required on the farm first.
2. Estimate the total quantity of this silage needed.
3. Calculate the area of first and subsequent cuts needed to produce this silage.
4. Mark on the farm map and set targets for spring grazing, fertiliser, cutting date.
5. Manage the remaining area to produce silage of standard quality.

Flexibility is needed around cutting date management, and each farm should develop a plan that suits its own scale, facilities, and stock type. For example, a farm carrying spring-calv­ing suckler cows plus some finishing cattle may take an early-cut of high DMD bales in mid- May on 20-30% of silage area, with the remainder of first-cut taken at 67-68% DMD in early June for feeding to dry cows.

Table 2 outlines the potential farm-scale value of taking this approach to achieve the correct target silage DMD. In this simple example, a farm with 40 weanlings and 40 forward store cattle requires 350 silage bales for a standard winter. The cost of total winter concentrates required to maintain target performance is reduced by 47% by moving from national aver­age silage quality to target silage quality for the stock type on hand.

Table 2. Effect of silage quality (dry matter digestibility, DMD) on winter concentrate costs for a calf-to-beef farm

Management guidelines for cost-effective grass silage production

Fertiliser and lime

The first step to improving silage yield and quality on most beef farms is to take soil samples and develop a field-by-field fertilizer plan based on the phosphorus (P), potassium (K) and lime requirements (Table 3). Treat P and K separately as silage fields may be adequate for one nutrient but be lacking in the other. Reduce the N application rate by 20-25 kg per ha for old pastures. Soil pH is often the first limiting factor for silage yield so ensure the target pH 6.3 is met. Apply lime through summer/autumn but avoid for 3-4 months before silage cutting as it may adversely affect the fermentation process.

Timing of silage cutting date

Swards should be managed such that good grass DM yields (4.8 to 5 t DM) are present at or before grass heading date. A decision can then be made whether to harvest at high DMD or delay beyond heading date to increase yield (to >6.0 t DM per ha) of a ‘maintenance-level’ feed. Timely fertilizer nitrogen (N) application and closing is important in respect of silage cutting date.

A useful guide for fertiliser N is that grass uses 2.5 kg N (2.0 units) per day on average, so final N should be applied approxi­mately 50 days before planned cutting date. However, the crop may still be safely harvested sooner depending on nitrate and sugar levels. If weather conditions are otherwise suitable, test the grass crop rather than sticking rigidly to the ‘2-unit rule’. Wilting the crop to >28% DM aids preservation if nitrate readings are high.

Table 3. Fertiliser nutrient application rates guidelines for first cut silage (kg/ha) 

Grazing in spring

To achieve good quality silage in May, it is essential that the sward is clean and green to the base in early March. Graze to <4cm residual in February/March before ap­plying fertilizer for silage. A similar effect can be achieved by tight grazing with young stock in late autumn. Swards with yellow/dead material must be grazed off otherwise silage DMD may be reduced by up to 6-7 percentage points. Re-seeded swards should have been grazed at least twice before closing for silage.

Achieving good preservation

Good preservation occurs when lactic acid bacteria present on the grass crop ferment available sugars to lactic acid. This causes a decline in pH which pre­serves the feed value of the stored silage. High available sugars, low buffering capacity and air-free (anaerobic) conditions are necessary for achieving good preservation. Grass sugars content is more critical to good preservation than nitrate readings. Ideal conditions for high sugars are ryegrass swards, dry sunny weather, cool nights and mowing in the afternoon. Add a sugar source (e.g. molasses) if conditions are good but sugars readings are low.

Under good ensiling conditions, there is no clear benefit to using additives such as inoculants. Adding inoculants will not significantly improve feed value if the standing grass crop is of poor quality. Where wilting is likely to be of benefit, reaching the target DM of 28-32% is a function of swath type and duration of drying. Dry matter will not increase sufficiently in large rows (>3 metres), even if left for 48 hours. Grass tedded out and left for more than 36 hours in good conditions may become be too dry (>40% DM) for pit silage. There is no advantage to wilting beyond 32% DM.

Reseeding

Old permanent pasture with low perennial ryegrass content is less responsive to fertiliser nutrients for first-cut crops, leading to delayed harvest and poor DMD. Lower sugar content makes preservation more difficult. The decision to reseed should be based on sward composition and performance. A rule of thumb is that silage ground should be reseeded every 8-10 years (5-6 years for multiple-cut systems). Many farms do not reach this target, especially if silage ground is on short-term lease. Reseeding is unlikely to be successful if soil fertility and post-emergence management to promote tillering and weed control are lacking.

Managing DM losses

Reducing DM losses at ensiling and feed-out is often overlooked as means of improving efficiency. These losses range from 15-30% of standing crop DM, which can significantly increase the cost per tonne harvested and the requirement for purchased feed. The main sources of DM loss are poor aerobic stability, failure to seal and maintain pits/bales fully, excessive exposure to air across the silage pit face, and waste at the feed barrier.

Joe Patton - Teagasc, Grange Animal & Grassland Research and Innovation Centre, Dunsany, Co. Meath